Heat exchanger for cooling a hot gas that contains solid particles

ABSTRACT

A heat exchanger for cooling a hot gas that contains solid particles, comprising heat exchanger tubes through which the hot gas flows, with the tubes being surrounded by a casing, and with ends of the tubes being welded, via weld seams, into bores of respective tube plates disposed at the ends of the casing. A protective layer coats the end face of the gas inlet side tube plate, an inner wall of the bores, the weld seams, and an inlet region of the heat exchanger tubes. The protective layer comprises a metallic adhesive layer, a high temperature and erosion resistant ceramic layer, and a high temperature and erosion resistant metal layer disposed between the adhesive layer and the ceramic layer.

BACKGROUND OF THE INVENTION

The instant application should be granted the priority date of Dec. 21,2004, the filing date of the corresponding European patent application04030220.0.

BACKGROUND OF THE INVENTION

The present invention relates to a heat exchanger for cooling a hot gasthat contains solid particles.

A heat exchanger of this type is known from EP 0 567 674 B1, and servesfor cooling synthetic gas produced in a coal gasification unit. With theknown heat exchanger, the tube plate on the gas inlet side is coveredwith a ceramic layer to protect against erosion and high temperaturecorrosion. The ceramic layer is comprised of individual ceramic sleevesthat are disposed next to one another and that in the upper part haveright-angled outer edges that abut one another, and in the lower parthave an opening, which extend into the heat exchanger tubes. Below thesleeves, on the tube plate, the weld seam and the tube inlets, is aprotective layer comprised of a metallic adhesive layer and a ceramiclayer. This protective layer becomes operational if one or more of thesleeves are destroyed.

It is an object of the present invention to simplify a heat exchanger ofthe aforementioned general type, and to provide more effective erosionprotection.

BRIEF DESCRIPTION OF THE DRAWINGS

This object, and other objects and advantages of the present invention,will appear more clearly from the following specification in conjunctionwith the accompanying schematic drawings, in which:

FIG. 1 is a longitudinal cross-sectional view through the lower portionof a heat exchanger;

FIG. 2 is an enlarged view of the encircled portion Z in FIG. 1;

FIG. 3 shows a protective layer; and

FIG. 4 is a plan view onto the tube plate of the heat exchanger of FIG.1.

SUMMARY OF THE INVENTION

The heat exchanger of the present application comprises heat exchangertubes through which the hot gas flows, with the heat exchanger tubesbeing surrounded by a casing, and with ends of the heat exchanger tubesbeing welded, via weld seams, into bores of respective tube plates thatare disposed at the ends of the casing; the heat exchanger alsocomprises a protective layer that coats the end face of the gas inletside tube plate, an inner wall of the bores, the weld seams, and aninlet region of the heat exchanger tubes, with the protective layercomprising a metallic adhesive layer, a high temperature and erosionresistant ceramic layer, and a high temperature and erosion resistantmetal layer disposed between the adhesive layer and the ceramic layer.

During the course of a coating process, the combination or compositeprotective layer can be applied to all endangered areas, and offers anoptimum protection against erosion not only when the solid particlesstrike at right angles but also when they strike at an inclination. Ithas been surprisingly shown that when solid particles strike at an angleof 90 degrees relative to the tube plate, a metallic protective layer ismore resistant to erosion than is a ceramic protective layer. However,when the strike angle is 45 degrees relative to the tube plate, in otherwords with an inclined strike, for example onto the weld seam, a ceramiclayer demonstrates a better resistance to erosion than does the metalliclayer.

Further specific features of the present application will be describedin detail subsequently.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring now to the drawings in detail, only the inlet side portion ofa heat exchanger for the cooling of reaction gas is shown in FIG. 1. Theheat exchanger comprises a tube bundle of straight heat exchanger tubes1 that are held in a respective tube plate 2 at each end of the tubebundle. The tube bundle is surrounded by an outer casing 3 that togetherwith the respective tube plates 2 delimits an inner chamber throughwhich flows boiling water that is under high pressure. A respective endchamber 4 adjoins the tube plate 2 on the illustrated gas inlet side andon the non-illustrated gas outlet side; the end chamber 4 is providedwith a connector 5 for the supply or withdrawal of the gas. The endchamber 4 widens conically from the connector 5 to the diameter of thetube plate 2. All of the components of the heat exchanger are made of ahigh-temperature steel.

Bores 6 pass through the tube plate 2, and the heat exchanger tubes 1are respectively concentrically inserted into the bores 6 and are weldedto the tube plate 2 via a weld seam 7 (see FIG. 2). The weld seam 7 isdisposed at the inner edge of the heat exchanger tube 1 and is embodiedas a concavely curved fillet weld. The hot gas that is introducedthrough the end chamber 4 encounters the tube plate 2 and flows throughthe bores 6 of the tube plate, along the weld seam and into the heatexchanger tubes 1. The solid particles carried along by the gas strikethe end face of the tube plate 2 at right angles and strike the weldseam 7 at an angle, thus leading to erosion at those locations. Erosionalso occurs in the inlet region of the heat exchanger tubes 1 due toturbulence. To protect against erosion, the end face of the tube plate2, the weld seam 7 at the inner edge of each heat exchanger tube 1, andthe inlet region 1 a of the heat exchanger tubes 1 are covered with atriple-layer protective layer 8.

As shown in FIG. 3, the protective layer 8 comprises an adhesive layer 9that is applied to the surface of the tube plate 2, to the weld seam 7at the inner edge of the heat exchanger tube 1, and to the inner side ofeach heat exchanger tube 1 in the inlet region 1 a. The adhesive layer 9serves as an adhesive agent for the following layers, which form theactual erosion protection. Applied to the adhesive layer 9 is a hightemperature resistant and erosion resistant metal layer 10, and a hightemperature resistant and erosion resistant ceramic layer 11 is appliedto the metal layer 10.

The individual layers are applied by flame spraying. The metal layer 10and the adhesive layer 9 each comprise a nickel-based alloy that isalloyed with one or more of the elements aluminum, cerium, iron,molybdenum and silicon. The ceramic layer 11 is comprised of zirconiumoxide stabilized with calcium.

The overall protective layer 8 has a thickness of 0.5 to 1.5 mm,preferably approximately 1 mm. By way of example, the adhesive layer 9has a thickness of about 0.1 to 0.5 mm, preferably 0.2 mm, the metallayer 10 has a thickness of approximately 0.2 to 0.8 mm, preferably 0.4mm, and the ceramic layer has a thickness of approximately 0.1 to 0.6mm, preferably 0.3 mm.

The specification incorporates by reference the disclosure of Europeanpriority document 04030220.0 filed 21 Dec. 2004.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

1. A heat exchanger for cooling a hot gas that contains solid particles,comprising: a casing; respective tube plates disposed at ends of thecasing; heat exchanger tubes through which said hot gas flows, whereinsaid heat exchanger tubes are surrounded by said casing, and whereinends of said heat exchanger tubes are welded into bores of said tubeplates via weld seams; and a protective layer that coats: an end face ofthat one of said tube plates disposed on a gas inlet side, an inner wallof said bores, said weld seams, and an inlet region of said heatexchanger tubes, and wherein said protective layer comprises a metallicadhesive layer, a high temperature and erosion resistant ceramic layer,and a high temperature and erosion resistant metal layer disposedbetween said adhesive layer and said ceramic layer.
 2. A heat exchangeraccording to claim 1, wherein each of said metal layer and said adhesivelayer is comprised of a nickel-based alloy that is alloyed with at leastone of aluminum, cerium, iron, molybdenum and silicon.
 3. A heatexchanger according to claim 1, wherein said ceramic layer is comprisedof zirconium oxide stabilized with calcium.
 4. A heat exchangeraccording to claim 1, wherein said protective layer has an overallthickness of from 0.5 to 1.5 mm.
 5. A heat exchanger according to claim4, wherein said adhesive layer has a thickness of from 0.1 to 0.5 mm,said metal layer has a thickness of from 0.2 to 0.8 mm, and said ceramiclayer has a thickness of from 0.1 to 0.6 mm.
 6. A heat exchangeraccording to claim 5, wherein said adhesive layer has a thickness ofabout 0.2 mm, said metal layer has a thickness of about 0.4 mm, and saidceramic layer has a thickness of about 0.3 mm.